Thermoelectric devices, namely thermoelectric power generators and coolers, have emerged as promising green technology. In general, thermoelectric devices offer the ability to convert waste-heat energy into electrical power or provide cooling from a solid state device. Applications of thermoelectric devices range from electronic thermal management, to solid state refrigeration, to power generation from waste heat sources. The figure-of-merit (ZT) of a thermoelectric material is a dimensionless unit that is used to compare the efficiencies of various materials. The figure-of-merit (ZT) is determined by three physical parameters, namely, thermopower α (also known as a Seebeck coefficient), electrical conductivity σ, thermal conductivity k, and absolute temperature T.
  ZT  =                              α          2                ⁢        σ            k        ⁢          T      .      
Maximum ZT in bulk thermoelectric materials is governed by the intrinsic properties of the material system. Most candidates require low thermal conductivity as the driving force for enhanced ZT because of the inverse relationship between the Seebeck coefficient and electrical conductivity. This interdependence and coupling between the Seebeck coefficient and the electrical conductivity have made it difficult to increase ZT>1, despite nearly five decades of research.
While the intrinsic properties of the thermoelectric material are the primary factor that drives the efficiency of a thermoelectric device, performance is also limited by both parasitic electrical and thermal resistances present in the thermoelectric device. The parasitic electrical resistance is primarily due to a barrier to current flow that forms when an external metal electrode is applied to the surface of the thermoelectric material. A barrier formed at the metal-thermoelectric interface (which is a metal-semiconductor interface) introduces resistance that is detrimental to the performance of the thermoelectric device.
The ideal ohmic contact to a semiconductor material follows the relationship:
            ρ      c        =                            ∂          V                          ∂          J                    ⁢              |                  V          =          0                    ⁢              Ω        ·                  cm          2                      ,where ρc is a resistivity of the ohmic contact, J is current density, and V is voltage. To maintain a linear relationship between the current and voltage as illustrated in FIG. 1, it is necessary to avoid all non-linear behavior of the current with respect to the applied voltage as shown in FIG. 2. A barrier at the metal-semiconductor interface is formed due to the difference of work functions and electron affinities between the metal electrode and the semiconductor material. In the case of an n-type semiconductor material in intimate contact with a metal layer, the Schottky barrier height φb depicted in the band diagram of FIG. 3 can be calculated by the equation:φb=φm−χ, for an n-type semiconductor materialwhere φm is a metal workfunction of the metal layer and χ is an electron affinity of the semiconductor material. As illustrated in FIG. 4, for a p-type semiconductor material, the barrier height φb is given by the difference in the valence band edge of the semiconductor material and the Fermi energy in the metal:
            ϕ      b        =                            E          g                q            +      χ      -              ϕ        m              ,for a p-type semiconductorwhere Eg is the semiconductor bandgap and q is the electronic charge. Conduction of carriers over or through the barrier determines the value of the resistivity ρc of the ohmic contact. As such, reduction of the barrier height φb is the primary driver for obtaining low resistance contacts.
As such, there is a need for systems and methods for reducing the barrier height φb at an interface between a metal and a semiconductor material to provide a low resistivity electrical contact.